Cache in Nero Burning Rom

Using Nero to copy discs, However when disc copying is completed Windows reports a loss on my hard disc of around 400 mb.I,ve checked the settings in the nero configure option and changed the folder to check that the cache is being burned back to the CD.All this seems to work ok but windows still reports a loss of 400mb.The strange thing is thatNero reports the disc usage as being the same asbefore i started the copying process. ie no loss of hard disc space.Anyone else encountered this problem?